1. Field of the Invention
The present invention relates generally to the field of illumination. More particularly, the present invention relates to illumination of flat panel displays using elongate fluorescent light sources.
2. Background Information
Miniaturization has been a significant theme in the advance of information technology. One very important miniaturization advance has been the development of flat video display screens, which are capable of supplanting bulky cathode ray tube (CRT) video display screens.
This new display technology is commonly called flat panel display. Flat panel display technology has found applications in laptop computers, handheld personal digital assistants, desktop computer monitors, and flat panel televisions. The most obvious advantage of flat panel display over bulky CRT displays is space savings. However, it has been a developmental struggle for flat panel displays to efficiently match the brightness characteristics of CRTs. To come even close to the brightness performance of CRTs, flat panel displays generally need some sort of illumination structure added.
Flat panel displays fall into several broad categories, based on the type of illumination they employ. Some flat panel displays are internally self light emitting. An example of this category is a gas plasma display. Other flat panel displays are reflective. Flat panel displays in this category illuminate by reflecting an external light source back out from the display. Another category of flat panel displays are those that are transmissive. These displays transmit light through the display from a light source such as an edge light or a direct back light. A hybrid category of displays combine the actions of reflective displays and transmissive displays.
Miniature fluorescent bulbs are used as light sources in most flat panel display lighting applications. Miniature fluorescent bulbs are generally cylindrical and thin, about the diameter of a piece of spaghetti. Light from these bulbs is typically reflected by a lightweight material, such as white plastic, white polyester film (e.g., MYLAR(trademark)), or metallized polyester film (e.g., SILVERLUX(trademark)). The amount of power consumed by the lighting structure to obtain a desired level of display brightness is affected by the type of fluorescent bulb employed (hot cathode, cold cathode), the number of bulbs used, and the reflection efficiency of any reflecting structures used.
Direct back-lit illumination is a prior art transmissive illumination scheme that places an array of compact fluorescent directly behind an LCD panel. This tends to consume a large amount of energy because it requires a large number of bulbs to provide uniform illumination across the back of the LCD panel.
Illumination structures of the reflective, transmissive, and hybrid categories all use reflection structures of one sort or another. Two problems with prior art reflection structures that harm efficiency are (1) losses caused by leaking of light from the reflector and (2) losses caused by dissipation of light energy due to excessive bounces. The first problem can be characterized as the need to minimize light energy leakage loss. The second problem can be characterized as the need to minimize light energy dissipation loss.
Thus, what is needed is a reflecting scheme for use in flat panel illumination structures that minimizes losses of light energy due to both leakage and dissipation. What is also needed is a scheme to efficiently illuminate a flat panel display using miniature fluorescent bulbs.
It is an object of the present invention to provide an illumination structure for a flat panel display that maximizes efficient utilization of all the light energy emerging from the light sources.
It is another object of the present invention to provide a fluorescent illumination structure for a flat panel display that maximizes efficient utilization of all the light energy generated.
It is yet another object of the present invention to provide an edge-lit compact fluorescent bulb illumination structure that maximizes efficient utilization of all the light energy generated.
It is still another object of the present invention to provide a process for manufacturing an efficient edge-lit fluorescent illumination structure.
It is a further object of the present invention to provide a reflecting scheme for use in flat panel illumination structures that minimizes losses of light energy due to both leakage and dissipation.
It is a still further object of the present invention to maximize light efficiency from fluorescent bulbs while controlling heat transfer.
It is an additional object of the present invention to provide an illumination scheme that may be adapted to a wide variety of displays.
It is also an object of the present invention to provide an illumination scheme that can be implemented in a simple manner.
Some of the above objects are obtained by a device for illuminating a flat panel display. The illuminating device has a flat light guide with light input edges and a light output surface, and light sources disposed at the light input edges. The illuminating device also has a layer of expanded PTFE wrapped closely around the light sources, conforming to their exterior surface, and spread across a back surface of the flat light guide. The illuminating device further has one or more reflector film layers wrapped over the layer of expanded PTFE. Light is emitted from the light output surface when the light sources are energized.
Others of the above objects are obtained by a method for manufacturing an illumination device. The method includes disposing a light source at a light input edge of a flat light guide, and wrapping a layer of expanded PTFE closely around the light source. The method further includes spreading the layer of expanded PTFE across a back surface of the flat light guide, and wrapping one or more reflector film layers over the layer of expanded PTFE. Preferably, a layer copper tape is wrapped over the one or more reflector film layers.